406 CELLEPOKIDuE. 



drical branches of nearly equal thickness throughout/' 

 In the minute characters the two forms essentially agree : 

 the only difference at all worth consideration is, that the 

 cells are less ventricose and crowded in the attenuata 

 variety, and the surface, as a consequence, smoother. But 

 towards the extremity of the branches this character is less 

 marked, and there is an approach towards the normal con- 

 dition. The stems are in all cases comparatively smooth 

 towards the bottom (i. e. in the older portions) ; and in the 

 attenuata form a larger proportion of the zoarium seems to 

 be in this state. I believe that this variety is more highly 

 calcined than the normal form, and that the peculiarity in 

 its appearance is partly due to this circumstance. I have 

 already referred to the dense white crust which occasion- 

 ally forms over C. dichotoma, and by which the ovicells 

 are in some cases partially invested; and the variety 

 seems to have undergone a similar change. 



The small aviculafia are present on C. attenuata, and 

 exhibit exactly the same characters as on the normal di- 

 chotoma, but are somewhat less numerous. Mr. Alder 

 seems not to have met with the spatulate avicularia at all ; 

 but though extremely rare in the specimens I have seen, 

 they are not altogether absent. The peculiarities of C. 

 attenuata, which he has noted with characteristic quick- 

 ness and accuracy, are certainly those of a variety and not 

 of a species. 



c. Orifice with a sinus below ; zoarium incrusting. 

 CELLEPORA AVICULARIS, Hincks. 



Plate LIV. figs. 4-6. 



CELLEPORA AVICULARIS, Hincks, Quart. Journ. Micr. Sc., Zoophytol. viii. 

 278; Proc. Dubl. Un. Zool. & Bot. Assoc. ii. pt. 1, 77; 

 Devon Cat., Ann. N. H. ser. 3, ix. 304 (48 sep.), pi. xii. 

 fig. 6: Norman, Shetland Pol., Rep. B. A. 18(58, 308. 



